Last week Ars Technica chose the winners for their science video contest in December:
http://arstechnica.com/science/news/2011/02/ars-announces-the-science-video-contest-winners.ars
These videos were fun to watch, and they ALL succeed in teaching you something about science while entertaining you.
Two videos explain the concept of a fourth dimension. One of them has an excellent soundtrack and the other one has a really good narration.
There was also a video about the Doppler effect!! That's one of the physics concepts that is the most fun to explain to others...and in that video it looks really good when you animate the Doppler effect.
To explain how antibiotics work, one video animates M&Ms and Twizzlers to great effect.
Last but not least the Large Hadron Collider is explained without any talking. That one was exciting to watch. When they show the "99.9991%"-ish number, are they talking about the speed at which the protons are accelerated?
Man, it would be so fun to pull off a video on this level...